The postnatal developmental expression pattern of urocortin in the rat olivocerebellar system

Gold-substituted Silver-intensified Peroxidase Immunolabeling for FIB-SEM Imaging

Modern electron microscopy offers a wide variety of tools to investigate the ultrastructural organization of cells and tissues and to accurately pinpoint intracellular localizations of macromolecules of interest. New volumetric electron microscopy techniques and new instrumentation provide unique opportunities for high-throughput analysis of comparatively large volumes of tissue and their complete reconstitution in three-dimensional (3D) electron microscopy. However, due to a variety of technical issues such as the limited penetration of label into the tissue, low antigen preservation, substantial electron density of secondary detection reagents, and many others, the adaptation of immuno-detection techniques for use with such 3D imaging methods as focused ion beam-scanning electron microscopy (FIB-SEM) has been challenging. Here, we describe a sample preparation method for 3D FIB-SEM, which results in an optimal preservation and staining of ultrastructural details at a resolution necessary for tracing immunolabeled neuronal structures and detailed reconstruction of synapses. This technique is applicable to neuronal and non-neuronal cells, tissues, and a wide variety of antigens.

Corticotropin-releasing hormone receptor-1 in cerebral microvessels changes during development and influences urocortin transport across the blood-brain barrier

In this study we tested the hypothesis that receptor-mediated transport of urocortin across the blood-brain barrier (BBB) undergoes developmental changes. Urocortin is a peptide produced by both selective brain regions and peripheral organs, and it is involved in feeding, memory, mood, cardiovascular functions, and immune regulation. In BBB studies with multiple-time regression analysis, we found that neonatal mice had a significant influx of (125)I-urocortin. By contrast, adult mice did not transport urocortin across the BBB. Quantitative RT-PCR showed that corticotropin-releasing hormone receptor (CRHR)-1 was developmentally regulated in enriched cerebral microvessels as well as hypothalamus, being significantly higher in neonatal than adult mice. This change was less dramatic in agouti viable yellow mice, a strain that develops adult-onset obesity. The level of expression of CRHR1 mRNA was 33-fold higher in the microvessels than in hypothalamic homogenates. The mRNA for CRHR2 was less abundant in both regions and less prone to changes with development or the agouti viable yellow mutation. Supported by previous findings of receptor-mediated endocytosis of urocortin, these results suggest that permeation of urocortin across the BBB is dependent on the level of CRHR1 expression in cerebral microvessels. These novel findings of differential regulation of CRH receptor subtypes help elucidate developmental processes in the brain, particularly for the urocortin system.

Postnatal developmental profile of urocortin 1 and cocaine- and amphetamine-regulated transcript in the perioculomotor region of C57BL/6J mice

Urocortin 1 (Ucn 1) is an endogenous corticotropin releasing factor (CRF)-related peptide. Ucn 1 is most highly expressed in the perioculomotor urocortin containing neurons (pIIIu), previously known as the non-preganglionic Edinger-Westphal nucleus (npEW). Various studies indicate that these cells are involved in stress adaptation and the regulation of ethanol (EtOH) intake. However, the developmental trajectory of these neurons remained unexamined. Expression of the cocaine- and amphetamine-regulated transcript (CART), which co-localizes with Ucn 1 in the perioculomotor area (pIII) has been examined prenatally, but not postnatally. The goal of the current study was to characterize the ontogenetic profile of Ucn 1 and CART during postnatal development in C57BL/6J (B6) mice. B6 mice were bred, and brains were collected at postnatal days (PND) 1, 4, 8, 12, 16, 24 and 45. Brightfield immunohistochemical staining for Ucn 1 and CART showed that Ucn 1-immunoreactivity (ir) was absent at PND 1, while CART-ir was already apparent in pIIIu at birth, a finding indicating that although the pIIIu neurons have already migrated to their adult position, Ucn 1 expression is triggered in them at later postnatal stages. Ucn 1-ir gradually increased with age, approaching adult levels at PND 16. This developmental profile was confirmed by double-immunofluorescence, which showed that Ucn 1 was absent in CART-positive cells of pIII at PND 4 and that Ucn 1 and CART are strongly but not completely co-localized in pIII at PND 24. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis confirmed that Ucn 1 mRNA levels are significantly lower at PND 4 and PND 12 than in adult animals. The lack of brain Ucn 1 immunoreactivity at birth and the gradual postnatal increase in Ucn 1 in pIIIu suggests that this peptide plays a greater behavioral role in adulthood than during the early postnatal development of an organism.

Stimulation of the inferior olivary complex alters the distribution of the type 1 corticotropin releasing factor receptor in the adult rat cerebellar cortex

In a previous study, it was shown that populations of climbing fibers, derived from the inferior olivary complex (IOC) contain the peptide corticotropin releasing factor (CRF) and that the expression of this peptide in climbing fibers could be modulated by the level of activity in olivary afferents. The intent of this study was to determine if there was comparable plasticity in the distribution of the type 1 CRF receptor (CRF-R1) in the cerebellum of the rat. Our results indicate that CRF-R1 was localized primarily to Purkinje cell somata and their primary dendrites and granule cells. In addition, scattered immunolabeling was present over the somata of Golgi cells, basket cells and stellate cells, as well as Bergmann glial cells and their processes. IOC stimulation for 30 min at 1 Hz increased CRF-R1 expression in molecular layer interneurons and processes of Bergmann glial cells. Little to no effect on CRF receptor distribution was observed in Purkinje cells, granule cells, or Golgi cells. IOC stimulation at 5 Hz however, increased CRF-R1 expression in the processes of Bergmann glial cells while decreasing its expression in basket, stellate and, to some extent, in Purkinje cells. The present results suggest that there is activity-dependent plasticity in CRF-R1 expression that must be considered in defining the mechanism by which the CRF family of peptides modulates activity in cerebellar circuits. The present results also suggest that the primary targets of CRF released from climbing fibers are Bergmann glial cells and interneurons in the molecular layer. Further, interneurons responded with a decrease in receptor expression following more intense levels of stimulation suggesting the possibility of internalization of the receptor. In contrast, Bergmann glial cells showed an increased expression in receptor expression. These data suggest that CRF released from climbing fibers may modulate the physiological properties of basket and stellate cells as well as having a heretofore unidentified and potentially unique effect on Bergmann glia.

Expression of cocaine- and amphetamine-regulated transcript (CART) peptides at climbing fibre-Purkinje cell synapses in the rat vestibular cerebellum

Cocaine- and amphetamine-regulated transcript (CART) peptides have a wide CNS distribution and appear to play an important role in a number of physiological processes including reward and reinforcement, feeding, locomotion, stress responses and perception of pain. We have further investigated the expression of CART peptides in rat cerebellum, using multiple fluorescent antibodies. Dense fibre-like immunofluorescence was observed in the molecular layer of the vestibular cerebellum (paraflocculus and lobes IX and X of the vermis). There was little or no immunofluorescence in any other region of the cerebellum (vermis or hemispheres). The immunofluorescence in lobes IX and X of the vermis showed a parasagittal banding pattern, with one medial and two lateral bands. We have provided several lines of evidence that CART peptides are expressed by climbing fibres: (1) There is CART peptide immunofluorescence in the inferior olivary complex, the source of climbing fibres. (2) No cerebellar cell bodies were labelled by the CART peptide antibody. (3) The developmental profile of CART peptide expression was consistent with climbing fibre development and finally (4) triple antibody labelling revealed co-expression of CART peptides with VGluT2 (the glutamate transporter at climbing fibre synapses) at boutons innervating calbindin D-28K labelled proximal Purkinje cell dendrites. Analysis of VGluT2 and CART peptide labelling in more detail showed that not all climbing fibres in the vestibular cerebellum expressed CART peptides but those fibres which did express CART peptides were immunofluorescent at all Purkinje cell synapses.

Cellular localization of the full-length isoform of the type 2 corticotropin releasing factor receptor in the postnatal mouse cerebellar cortex

Corticotropin releasing factor (CRF) and its cognate receptors, defined as Type 1 and Type 2 have been localized within the cerebellum. The Type 2 CRF receptor (CRF-R2) is known to have both a full length (CRF-R2alpha) and a truncated (CRF-R2alpha-tr) isoform. A recent study documented CRF-R2alpha primarily in Bergann glia and astrocytes, as well as in populations of Purkinje cells in the adult cerebellum. The goal of the present study is to determine if CRF-R2alpha is present in the postnatal cerebellum, and if so to describe its cellular distribution. RT-PCR data showed that CRF-R2alpha is expressed in the mouse cerebellum from birth through postnatal day 21. Between birth and P14, CRF-R2alpha-immunoreactivity was localized within the somata of Purkinje cells, and migrating GABAergic interneurons. GFAP-immunoreactive astrocytes, including Bergmann glia, also expressed CRF-R2alpha-immunoreactivity from P3-P14. There is a change, however, in CRF-R2alpha immunolabeling within neurons as the cerebellum matures. Compared to its expression in the adult cerebellum, Purkinje cells, and GABAergic interneurons showed more extensive CRF-R2alpha immunolabeling during early postnatal development. We postulate that CRF-R2alpha could be involved in developmental events related to the survival and differentiation of Purkinje cells and GABAergic neurons, whereas in the adult, this isoform of the CRF receptor family is likely involved in modulating Bergmann glia that have been shown to play a role in regulating the synaptic environment around Purkinje neurons.

Microzonal projection and climbing fiber remodeling in single olivocerebellar axons of newborn rats at postnatal days 4-7

An adult olivocerebellar axon ramifies into about seven climbing fibers that innervate single Purkinje cells arranged in a longitudinal microzone. To clarify the developmental basis of this projection, individual olivocerebellar axons were labeled with biotinylated dextran amine injected into the inferior olive in rats at postnatal days 4-7. The entire trajectories of single olivocerebellar axons and single terminal arbors of climbing fibers were reconstructed from serial sections of the cerebellum and medulla. Single axons ramified into climbing fibers that terminated in a narrow band-shaped area comparable to the adult microzone. This indicated that olivocerebellar microzones are predetermined. Terminal arbors of climbing fibers were remodeled from loose creeper type, through intermediate transitional type, into dense nest type. Each olivocerebellar axon had some 100 nascent climbing fibers in the creeper stage, whereas each axon had about 10 climbing fibers and about as many atrophic climbing fibers in the nest stage. This decrease indicated that overabundant nascent climbing fibers degenerate concomitantly with the remodeling of remaining climbing fibers. Atrophic terminal arbors and non-climbing fiber thin collaterals were considered the intermediate forms of degenerating climbing fibers. This remodeling and degeneration of climbing fibers may be related to the electrophysiological regression of climbing fiber-Purkinje cell synapses. The remodeling of climbing fibers occurred earliest in lobules VIII (caudal part) and IXa-b, and then in lobules IXc and X. The more developed granular layer in these areas compared to other areas suggests that the cortical environment triggers climbing fiber remodeling.